I've been shooting USPSA off and on for a few years, now. I'm not a "serious competitor", and I've not shot any classifiers. I shoot with either my duty gear or an OWB setup I use off duty. I would like to move to using my current AIWB setup, too.
My goals have been to pressure-test my actual "real-world" equipment, my gun-handling and my visual processing skills/ problem-solving skills, with someone else's course of fire. Plus, it's great fun.
So far, I've shot a G-17, Gen.4 (stock except Trijicon HD sights), a G-17 MOS (again stock, with a RMR and Ameriglo suppressor height sights added), and a G-19X (stock, with HD's), in USPSA matches. My best results thus far have been with the 17 MOS, winning Carry Optics once and placing well, nearly every time. I've actually beaten a couple of shooter's raw times on the same stage, while they were shooting pistol-caliber carbines. Possibly a fluke, but it still felt good in the validation department.
I haven't felt limited by my equipment, yet. My main limitations have been self-induced; mainly botching my stage plan and having to play "catch-up", which cost me time for reloads. I've always approached each stage with the goal of getting as many A-zone hits as possible, even if that means I had to shoot a bit slower. USPSA's scoring doesn't reward hosing the target at the expense of accuracy, like some other competitions. I don't think I've gotten to the point of maxing out my skills, where any aftermarket add-ons, like barrels, triggers, magwells, etc. would make a difference.
If I had advice for anyone starting this, it would be to worry less about equipment and concentrate on making good stage plans and shooting only as fast as you can hit. The speed will show up, as you improve your skills and you may find you can turn in some pretty good results, while enjoying yourself.